Filaments are ubiquitous structures in molecular clouds and play an important role in the mass assembly of stars. We present results of dynamical stability analyses for filaments in the infrared dark cloud G14.225-0.506, where a delayed onset of massive star formation was reported in the two hubs at the convergence of multiple filaments of parsec length. Full-synthesis imaging is performed with the Atacama Large Millimeter/submillimeter Array to map the {{{N}}}2{{{H}}} (1{--}0) emission in two hub- filament systems with a spatial resolution of ∼0.034 pc. Kinematics are derived from a sophisticated spectral fitting algorithm that accounts for line blending, large optical depth, and multiple velocity components. We identify five velocity coherent filaments and derive their velocity gradients with principal component analysis. The mass accretion rates along the filaments are up to {10}-4 {M}☉ {yr}}-1 and are significant enough to affect the hub dynamics within one freefall time (∼105 yr). The {{{N}}}2{{{H}}} filaments are in equilibrium with virial parameter α vir ∼ 1.2. We compare α vir measured in the {{{N}}}2{{{H}}} filaments, {NH}}3 filaments, 870 μm dense clumps, and 3 mm dense cores. The decreasing trend in α vir with decreasing spatial scales persists, suggesting an increasingly important role of gravity at small scales. Meanwhile, α vir also decreases with decreasing nonthermal motions. In combination with the absence of high-mass protostars and massive cores, our results are consistent with the global hierarchical collapse scenario.
Filaments are ubiquitous structures in molecular clouds and play an important role in the mass assembly of stars. We present results of dynamical stability analyses for filaments in the infrared dark cloud G14.225-0.506, where a delayed onset of massive star formation was reported in the two hubs at the convergence of multiple filaments of parsec length. Full-synthesis imaging is performed with the Atacama Large Millimeter/submillimeter Array to map the {{{N}}}2{{{H}}}+ (1{--}0) emission in two hub- filament systems with a spatial resolution of ~0.034 pc. Kinematics are derived from a sophisticated spectral fitting algorithm that accounts for line blending, large optical depth, and multiple velocity components. We identify five velocity coherent filaments and derive their velocity gradients with principal component analysis. The mass accretion rates along the filaments are up to {10}-4 {M}? {yr}}-1 and are significant enough to affect the hub dynamics within one freefall time (~105 yr). The {{{N}}}2{{{H}}}+ filaments are in equilibrium with virial parameter a vir ~ 1.2. We compare a vir measured in the {{{N}}}2{{{H}}}+ filaments, {NH}}3 filaments, 870 µm dense clumps, and 3 mm dense cores. The decreasing trend in a vir with decreasing spatial scales persists, suggesting an increasingly important role of gravity at small scales. Meanwhile, a vir also decreases with decreasing nonthermal motions. In combination with the absence of high-mass protostars and massive cores, our results are consistent with the global hierarchical collapse scenario.
